If you aren't moving at a snail's pace, you aren't moving at all. -Iris Murdoch

Wednesday, February 29, 2012

Brittle vs. Elastic

Okay, so we're wading into some rock mechanics with the intro class. One of the most important characteristics is how rocks respond to stress. If you've ever hit a rock with a hammer, you're probably aware of brittle behavior - where the rocks break into smaller pieces. If you've got the right kind of rocks (typically rocks under higher pressures and temperatures - like you see deep in the crust/mantle area) they might bend and flow. There are some other things that affect this brittle/ductile behavior. How quickly the stress is applied, for example. Hit the rock with a hammer and you might get broken pieces. Apply the same stress over a very long time and you might get the rock to bend.

This is rather hard to do with rocks, however. Silly Putty is a much more convenient material for those of us stuck on the earth's surface. Pull the silly putty slowly and it will stretch and flow. Pull on it quickly and you might get it to snap and break. Or, you could hit it with a hammer, which is not as easy as it sounds...